A number of high-precision mass flow measurement systems are useful in materials processing. These high-precision mass flow measurement systems may include, but are not limited to, mass flow controllers (MFCs) and mass flow meters (MFMs). While this disclosure applies to all mass flow measurement systems and methods, reference will only be made to MFCs hereafter for illustration purposes only and not by way of limitation.
It may be desirable and sometimes necessary to test or verify the accuracy of an MFC. One way to verify the accuracy of an MFC is through the use of a rate of decay, mass flow verifier (MFV) positioned upstream of the MFC under test.
Sometimes, however, measurement errors may occur due to structural aspects of the flow path that introduce undesirable pressure variations which affect the measurement of the MFV and MFC. For example, MFCs have a portion of the flow path between the flow sensor and the control valve called the “dead volume” which can introduce errors in flow measurement, especially if the MFC is a non-pressure insensitive (i.e., pressure sensitive) MFC which does not have a pressure sensor inside the MFC. The non-pressure insensitive MFC cannot compensate for the flow rate error caused by the pressure fluctuation. As fluid flows along the flow path from the flow verifier through the dead volume and out of the MFC, the dead volume may cause inaccuracies in the pressure measurements and ultimate flow verification.